The present invention relates generally to a method of controlling a mounting arrangement for an automotive power unit such as a hydraulic mount for vibration damping of an engine or transmission. More particularly, the invention is directed to a system and controller for a hydraulic mount assembly that features accelerometers to sense the relative acceleration between a vehicle engine and body, the relative acceleration values of which may be used by a control unit to alter the control characteristics of the mount.
Modern vehicle designs place an increasing demand for improved smooth running and driving comfort. To meet these requirements, there has been an increasing demand for further improved vibration damping or isolating characteristics of the engine mount. Minimizing the transmission of engine vibration at the bounce resonance frequency, i.e., the resonance frequency where the engine bounces most vigorously, to the frame is of particular interest, since it greatly impacts the smoothness of the ride comfort.
It is well known in the industry that the engine bounce frequency is a result of the body/engine properties. Thus for every change in the design of the body/engine (and hence the bounce resonance frequency), a new mount has to be designed.
A variety of engine mount assemblies are presently in use in the automotive industry to reduce the transmission of engine vibration to the car body. Examples of such vibration damping and/or isolation devices are vibration-absorbing, elastomeric automotive engine mounts. Hydraulic mounts combine the properties of elastomeric materials and viscous dampening properties of non-compressible hydraulic fluids and have been used in automobiles for decades. Hydraulic mounts are commonly elastomeric engine mounts enclosing a fluid-containing cavity. The cavity is separated into two chambers by a dividing plate where the plate contains an orifice to allow fluid to communicate between the two chambers. A pressure-receiving fluid chamber is formed between the orifice or partition plate and an elastic mount body, whereas an equilibrium chamber is formed between the plate and a diaphragm. These mounts are referred to as passive mounts (i.e., the dampening characteristics of which are a function of the design only).
Active mounts have more recently become known in the art. They provide electronic control of their dampening characteristics/behavior, and can typically exhibit responsive dampening behavior based on electronic input signals.
Active controllable dampening behavior of hydraulic mounts can be achieved by employing an electronically variable gate or valve to the orifice or track between the aforementioned fluid chambers. As the flow rate of fluid that is communicated between the chambers is altered, the dampening stiffness of the mount varies accordingly. The slow response time of mechanical valves or gates makes them less ideal for use in real-time tunable damping systems.
More recently, the use of controllable fluids such as electrorheological (ER) and magnetorheological (MR) fluids has been applied in engine mount designs. Examples of the use of MR hydraulic fluid dampers can be found in U.S. Pat. Nos. 5,284,330; 5,878,850 and 5,712,783. One example of an ER fluid mount can be found in U.S. Pat. No. 4,733,758. Magnetorheological fluids are materials that respond to an applied magnetic field with a dramatic change in the rheological behavior. The essential characteristic of these fluids is their ability to reversibly change from a free-flowing, linear, viscous liquid to a semisolid with controllable yield strength in milliseconds when exposed to a magnetic field. In MR engine mounts, the MR fluid is communicated via flow apertures in the separating plate between the two chambers where the fluid is exposed to a controllable magnetic field. As the MR fluid is exposed to the magnetic field, its sheer resistance increases and the dampening stiffness of the mount increases accordingly.
Active hydraulic MR mounts can be controlled by a current signal producing a proportional electromagnetic field in the track between the fluid chambers. The control signal is commonly produced by a controller unit utilizing one or more electrical control input signals. Typically, a sensor signal that is received by the controller will be proportional to a parameter such as vibratory motion (such as relative displacement, velocity or acceleration), but a sensor that measures mount fluid pressure, or other sensed dynamic properties can also be used. In complex control systems where the controller processes several such input signals to generate an output signal, the performance of the mount will depend greatly on the design and calibration of the system.
The use of MR and ER fluids in vibration damping mounts enables such mounts to produce real-time varying damping characteristics in response to supplied real-time control signals. It is well known in the art that successful damper performance for any vibration damping system is greatly dependent upon the particular control algorithm employed to vary the damper forces. Successful active damping of suspension systems and engine mounts in vehicles will typically require the controller to process several input signals from sensors such as relative displacement and/or its derivatives (velocity/acceleration), external force system disturbances and the like. One such control algorithm is presented in U.S. Pat. No. 4,953,089. Other examples of control algorithms for active vibration attenuation can be found in U.S. Pat. Nos. 3,807,678; 4,491,207; 5,712,783; 3,807,678 and 4,491,207 and references therein.
In designing such a control system, appropriate sensory input to the controller must be determined as well as the design of the control structure that is to be implemented in the controller device. An example of a controllable damper system and references to related patents can be found in U.S. Pat. No. 5,712,783.
It would be advantageous to provide a control system and method with the capability to control vibrations of various engine/frame assemblies without redesigning the system.
The present invention is directed to the need for redesigning engine mounts for changing body/engine characteristics. The current invention presents a system and method or algorithm for dynamically calibrating a mount type known as magnetorheological (MR) mounts where the dampening characteristics of the mount can be altered electronically without changing the design of the mount.
One aspect of the present invention includes a calibration control algorithm or method to determine the parameters of the controller. The real-time varying damping characteristics of the MR mount should exhibit optimal damping performance within a frequency window around the bounce frequency for a given body/engine design. It is therefore advantageous that the calibration algorithm allows the objective damping characteristics to be specified directly in the frequency domain. It is also desirable that the calibration algorithm has few tuning parameters and that it is robust with respect to convergence to an optimal calibration result.
Another aspect of the present invention may include the design of a control-loop structure that can be implemented in the controller such that the controller can produce a sufficient output control current signal to the magnetorheological control device of the mount. The output control signal is used to regulate the flow of MR fluid between the chambers so that maximum damping may be obtained in the net relative acceleration, at and around the bounce resonance frequency when subjected to external disturbances. External disturbances can be due to body acceleration transmitted by the road inputs through the wheels.
Another aspect of the present invention can include an algorithm for determining the parameters of the control-loop structure such that the controller produces sufficient output control current signal to the magnetorheological control device of the mount. The control device uses the control current signal to regulate the flow of MR fluid between the chambers so that maximum damping is obtained in the net relative acceleration, at and around the engine bounce resonance frequency when subjected to external disturbances due to body acceleration.
Another aspect of the invention provides a method of controlling a hydraulic mount of a vehicle engine including calibrating at least one tunable parameter of a control system of the mount based on an engine bounce resonant frequency, sensing a relative acceleration across the mount, generating a control signal responsive to the relative acceleration based on at least one tunable parameter and controlling the flow of MR fluid in the mount responsive to the control signal such that maximum vibration damping occurs at a predetermined band of frequencies.
The predetermined band of frequencies may occur at and around the resonance bounce frequency of the engine. Calibrating the tunable parameter may include tuning an objective function defined by a weighted sensitivity transfer function. The weighting function may be limited to the resonance bounce frequency. Calibrating the tunable parameter may include tuning an associated scalable factor. The associated scalable factor can be used to increase and decrease the magnitude of the weighting function.
Another aspect of the present invention provides a system for controlling a hydraulic vibration damping engine mount for a vehicle includes at least one mount, each mount defining a fluid chamber, means for sensing relative acceleration across each mount, a tunable control device operably connected to the sensing means for generating a control signal based on the sensed relative acceleration and maximized at a predetermined band of frequencies and a coil member positioned adjacent to the mount, the coil member operably connected to the control device for generating a magnetic field in the fluid chamber based on the control signal.
The sensing means can be a pair of accelerometers positioned such that a first accelerometer is placed on an engine of the vehicle and a second accelerometer is placed on a frame member of the vehicle. The at least one mount may include a first and a second mount. The first and second mounts may be placed between the engine and the frame in a spaced apart configuration. The mount may include a magnetorheological mount fluid. The coil may be positioned to control the flow of magnetorheological fluid between upper and lower chambers of each mount. The coil may include an annular coil positioned adjacent at least one passageway through a plate, the plate being positioned between the upper and lower chambers. The coil can be adapted to impart an increased shear resistance to the magnetorheological fluid when a current is passed through the coil.
Another aspect of the present invention provides a system for controlling a hydraulic mount of a vehicle engine including means for modifying at least one tunable parameter of a control system of the mount based on an engine bounce resonant frequency, means for sensing a relative acceleration across the mount, means for generating a control signal responsive to the relative acceleration based on the at least one tunable parameter and means for controlling the flow of MR fluid in the mount responsive to the control signal such that maximum vibration damping occurs at a predetermined band of frequencies.
Another aspect of the present invention provides a control system for a hydraulic mount for a vehicle including means for sensing a relative acceleration across the mount, means for generating a control signal corresponding to the relative acceleration, means for controlling the flow of MR mount fluid in the mount responsive to the control signal, means for tuning the control system such that maximum vibration damping occurs at and around the engine resonance bounce frequency.
The foregoing and other features and advantages of the invention will become further apparent from the following detailed description of the presently preferred embodiments, read in conjunction with the accompanying drawings. The detailed description and drawings are merely illustrative of the invention rather than limiting, the scope of the invention being defined by the appended claims and equivalents thereof.